1. Technical Field
The present invention generally relates to an electronic file sending method. More particularly, the present invention relates to a method of sending an encrypted electronic file.
2. Related Art
To send an electronic file via a communication network such as the Internet, the electronic file is generally attached to an electronic mail. This electronic file sending method has the following drawback. All of the data constituting the electronic mail remains in, for example, servers that relay the electronic mail and is easily accessed by a third person.
To avoid this problem, it is known in the art to encrypt the electronic file to be attached to the electronic mail (see Japanese Patent Application Publication No. 2007-306261). According to the technique disclosed in Japanese Patent Application Publication No. 2007-306261, a third person will have difficulties in accessing the content of the encrypted electronic file.
When the electronic file is encrypted to overcome the above-described drawback, the sender of the electronic mail needs to inform the receiver of the electronic mail of a password necessary to decrypt the encrypted electronic file. According to the technique disclosed in Japanese Patent Application Publication No. 2007-306261, while the electronic mail having an encrypted electronic file attached thereto is sent from a personal computer, the password necessary to decrypt the encrypted electronic file is sent from a mobile phone. Here, since the password is sent to a mobile phone network as it is, the password may possibly be accessed by a third person. Thus, the technique disclosed in Japanese Patent Application Publication No. 2007-306261 cannot securely communicate the password to the receiver.
When the above-mentioned electronic file sending method is continuously employed, in particular, over a long time period, both the sender and the receiver are required to manage the password.
The password tends to be vulnerable to dictionary attach (for example, in the case of a short character/number string or a meaningful character string), since the password is typically chosen by a human being. This tendency becomes particularly strong due to the above-mentioned necessity of the password management by both the sender and the receiver.